1. Field of the Invention
The present invention relates generally to the art of a vibration damping device for damping torsional vibrations, and especially to a vibration damping device having a pendulum mass held in a rotary member and oscillated by torque pulses of the rotary member.
2. Discussion of the Related Art
Rotary members such as a drive shaft and gears involving torque transmission between a prime mover to a driven member are vibrated inevitably by torque pulses, load fluctuations, friction etc. Vibration frequency of the rotary member is changed in accordance with a rotational speed, and vibration amplitude is increased by a resonance between an intrinsic vibration frequency of the rotary member itself and the torque pulses applied thereto. Consequently, noises would be increased and the system would be damaged. In order to avoid such disadvantages, according to the conventional art, a vibration damping device is widely used in power transmission systems.
For example, international publication WO 2013/128590 describes a vibration damping device. According to the teachings of WO 2013/128590, pendulum masses and coil springs are arranged concentrically so that the damping device can be downsized.
However, if a casing member is fixed to the rotary member by a rivet in the vibration damping device taught by WO 2013/128590, a long rivet is required and such long rivet may be deformed easily when a tail of a shaft is expanded. For this reason, a required fastening strength between those members may not be achieved.
The present invention has been conceived noting the foregoing technical problems, and it is therefore an object of the present invention is to fix a casing member covering a pendulum damper firmly by a rivet.